Field of the Invention
The present invention relates to a method of controlling the temperature of a joining area between two different plate-like materials in a continuous strip processing line for performing the coating, drying, baking, or cooling.
Description of the Prior Art
In a conventional continuous strip processing line of this kind, the nozzle pressure (a function of velocity of hot blast blown to a strip from nozzles) in a certain zone of a treating furnace is controlled by either a recirculation fan or a damper. For example, when a joining area between two plate-like materials (i.e., strips) each having a different thickness passes through such a zone, the temperature of a strip in the vicinity of the joining area inevitably deviates from a predetermined target value. In order to minimize the deviation from the target value, the nozzle pressure must be rapidly changed from an optimum value of the preceding strip to that of the following strip by raising the rate of change of the nozzle pressure. This nozzle pressure is represented as a function of the speed of hot air directed to the strip from nozzles and is generally controlled by regulating the rotational speed of the recirculation fan or the opening of the damper.
When the nozzle pressure is controlled by regulating the rotational speed of the recirculation fan, the motor power required to drive the recirculation fan must be increased under the influence of the inertia (GD.sup.2) of the recirculation fan itself, to increase the speed of changes in the nozzle pressure. If the recirculation fan is reinforced so as to endure high acceleration and deceleration, the inertia of the recirculation fan itself is required to be increased, thus causing a vicious circle necessitating the increase of the motor power. Accordingly, the speed of change of the practical nozzle pressure is naturally restricted.
On the other hand, when the nozzle pressure is controlled by adjusting the opening of the damper, the controllability of low nozzle pressure in a low air flow is lost or cannot be expected. In operation under the low nozzle pressure, the efficiency of the recirculation fan is relatively low, thus causing undesirable increase in power consumption per unit weight of a product.